When dilution refrigerators became available, experiments were possible down
to base temperatures as small as a few millikelvin. Leggett [1]}
had predicted that below a “crossover
temperature” a Josephson junction would enter a
macroscopic quantum state. Voss and Webb [2]} were the first to
claim confirmation of this conjecture with evidence based on observations
reaching \(5mK\)  and interpreted with the hypothesis of macroscopic quantum
tunneling (MQT) as the new mechanism for escape from the well.
